The present invention relates to equaliser circuits, and in particular to equaliser circuits for use in radio frequency (RF) signal receivers.
Integrated receivers require intermediate frequency filters for selectivity: attenuation of strong (adjacent channel) signals at carriers close to the carrier of the desired signal. A post-detection filter usually helps also in attenuating the first adjacent channel signal. There is a compromise between adjacent channel performance, sensitivity, and co-channel performance. The higher the required selectivity, the worse the co-channel performance and sensitivity.
Equalisers are well-known in transmission systems. Equalisers are usually implemented in digital technology. This solution is not very useful, since the demodulation, and bit-slicing (the decision whether a bit is a xe2x80x9c0xe2x80x9d or a xe2x80x9c1xe2x80x9d) is done in the analog domain. Shifting all this to the digital domain would increase the power consumption and increase the complexity.
It is therefore desirable to provide a simple equaliser that improves the sensitivity, co-channel performance and selectivity of a receiver.
It is also desirable in such circuits to be able to correct (or xe2x80x9ctunexe2x80x9d) for changes in temperature and component tolerance.
According to one aspect of the present invention, there is provided an equaliser circuit in which a resistance value and/or capacitance value can be tuned such that the overall performance is independent of component variation due to, for example, process spread and/or temperature variation.
According to another aspect of the present invention, there is provided an equaliser circuit which realizes the transfer function:       H    ⁢          (      s      )        =      R    ⁢          (                        k                      1            +            sRC                          -        1            )      
in which R is a resistance value, C is a capacitance value and k is the gain of an amplifier.
According to another aspect of the present invention, there is provided an equalizer circuit comprising transconductance elements, at least one of which is a tuneable element having operating parameters determined by a tuning voltage of the element.
According to another aspect of the present invention, there is provided an equaliser circuit realizing the transfer function:       H    ⁢          (      s      )        =                              R          2                          1          +                                    SR              2                        ⁢            C                              ⁢      k        -          R      1      
in which R1, R2 are respective resistance values, C is a capacitance value, and k is the gain of an amplifier.